Respuesta :
I'm assuming 24. I used process of elimination starting from common multiples that could be dovided by 4.
Answer:
24 years old
Step-by-step explanation:
3/4n +9= 1/4n +21
3/4n-1/4n = 21-9
2/4n = 12
2/4 · 4/2n = 12·4/2
n = 24